I recently wrote an artitle on multi-asset investing for Professional Wealth Management magazine which is part of the Financial Times Group.
Basically, the perfect storm of the financial crisis nullified the supposed diversification benefits of multi-asset class strategies, but it is argued that for a range of innovative featues, they can provide investors with a more efficient and effective diversification strategy.
For more details, please refer to the following web link.
http://www.pwmnet.com/news/get_file.php3/id/297/file/p23+pwm.pdf